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After passing Mercury the first time and making a trip around the Sun, Mariner 10 again flew by Mercury on September 21 at 1:59 PMPDT. This encounter brought the spacecraft in front of Mercury in the southern hemisphere.

Much of Mercury looks like the lunar highlands, a scene carved by billions of years of impact craters. This image (FDS 166724) was taken when Mariner 10 was near its closest approach to the planet during the second encounter, about 50,000 km. This image is found near the center of the area not imaged during the first encounter.

The Mariner 10 mission, managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, explored Venus in February 1974 on the way to three encounters with Mercury-in March and September 1974 and in March 1975. The spacecraft took more than 7,000 photos of Mercury, Venus, the Earth and the Moon.